How to assign PointerProperty in Operator through UI?
Aafter continuing researching, apparently operators can only take basic properties (e.g. string, bool, int, float), and PointerProperties only work if they’re stored within at the scene level (e.g. bpy.types.Scene) or inside a PropertyGroup.

So, short answer, it doesn't seem possible at this point (2.81a).

Anyways, my current workaround is making an EnumProperty on the panel that switches between the different instances of layers. Since the enum is stored at the scene level, all my operators can reference it freely and easily. It’s not as contained as I’d like, but it works.